148 



BLOOD. 



12 Enumeration of the Red Blood Corpuscles. 



Thoma-Zeiss Hsemaeytometep. This consists of : 



1. Dilution pipette, or mixer, having a bulb containing a glass 



bead for mixing. The stem is graduated from Ol to 1, 

 and to 101 above the bulb. 



2. Counting chamber, a cell with an outer rim, and a central 



platform, the latter ruled in squares ; each square has a 

 side of 1/20 mm , and hence an area of 1/400 mm square. 

 The film of fluid between the glasses is O'l mm thick 

 when the chamber is. covered, and consequently the 

 portion over each square is 1/4000 of a cubic millemetre. 

 Groups of 16 squares are separated by additional lines. 



FIG. 15. Thoma-Zeiss Haemacytometer. a and b the counting chamber, in which 

 W is the outer rim upon which the cover D rests. B central platform, and r the circular 

 trench which separates it from D. c divisions on B (x 30). S M mixing pipette for red 

 blood cells. 



Process : 



1. Puncture the finger freely. 



2. Draw blood up in the mixer to 0'5 or 1 on the stem of 



the pipette. Wipe the point dry. 



3. Draw in 3 p - c - salt solution to the mark 101 above the bulb, 



and mix the fluids by shaking. 



